But what about extreme obesity (BMI > 40)? A 2001 CHEST review of 117 patients suggested increased morbidity and mortality in this group.

Martino et al re-heated the data from a 2009 observational nutritional study in 355 ICUs in 33 countries. That was n=8,800, about half of whom were normal weight, and 520 of whom had BMI > 40. Multiple outcomes were pre-specified and recorded in the original epidemiologic study.

Unadjusted for confounders, those with extreme obesity had a reduced odds ratio for death of 0.77. After adjustment for confounders, there was no relationship between extreme obesity and excess mortality. However, extremely obese people had longer duration of mechanical ventilation and ICU length of stay (but not different hospital lengths-of-stay). Results could not be reported in days due to the methodology.